Spray device



J. T. KREMER June 13, 1950 SPRAY DEVICE File'd Dec. 20, 1945 INVENTOR 7'- (eaw e ATTOR Y Patented June 13, 1950 STAES SPRAY DQ'JE John Thad Kremer, Houston, Tex, asslgnor to The Texas Company, New York, N. Y., a corporation oi Delaware d Cla.

This invention relates to spraying devices of the spray-gun type .and more particularly to a device for spraying or coating the inner surface of small diameter tubes or cylinders. The prim cipal object of the invention is to provide a device which is readily portable, which is sufficiently smallin the over-all diameter of the gun portion to be positioned or moved back and forth within a tube or cylinder having an inside diameter of but a fraction of an inch, and which contains but one moving part so that it is comparatively simple of construction and rugged in operation.

There are instances where it is desirable to place a substantially uniform coating or layer of a substance on the inner surface of a relatively long tube having an inner diameter as small as one-half inch. As an example reference may be had to the copending application of Kenneth G Cl'lmrine, Serial No. 625,597, filed October 30, 1945, in which is described a method of preparing the cathodes of neutron detectors particularly at the proportional counter type. As stated in that application a detector may be formed of a plurality of cathode tubes of brass or other suitable metal, each tube having its inner surface coated with a layer of a neutron reactive substance such as boron carbide. Again, as stated in the application, while the boron carbide particles in a suitable carrier such as a low viscosity liquid adhesive maybe painted upon the cathode surface it has been found that a much more eflicient cathode will result if the boron carbide particles in an adhesive binder are placed on the cathode surface by means of a fine spray while the cathode is being rotated about its longitudinal axis. Where it is desired to form a coating of particles of a heavy, hard substance such as boron carbide by means of a. device of the spray gun type, the problem of abrasion by the particles is of course important. The device of the present invention has been devised to meet this problem and has been used very successfully in coating the inner surfaces of neutron detector cathodes with a layer of boron carbide particles, such a layer averaging about one mil in thickness.

In accordance with the invention an elongated tubular member is secured at one end to a re= ceptacle or hopper adapted to contain the mixture of the substance to be sprayed in a liquid carrier. The outer end of this tubular member is provided with the laterally extending nozzle, the opening in which may be but a few mils in diameter. Surroundingv the tubular member and spaced slightly therefrom is another tube or sleeve having at its outer end an opening slightly larger'than the nozzle and through which the mixture to be entrained and blown as a spray against the surface to be coated. An agitator member within the mixture tube maintains the mixture in a loose condition at all times during the spraying operation and the danger of the particles plugging the nozzle or stopping up the tube is therefore obviated.

For a better understanding of the invention reference may be had to the accompanying draw= ing in which:

Figure 1 is a vertical longitudinal sectional elevation through the device,

Figure 2 is an enlarged cross sectional view on line 2-2 of Figure 1 looking in the direction of the arrow,

Figure 3 is a similar enlarged cross sectional view of Figure l on the line 3-3 looking in the direction of the arrow, and

Figure 4 is a sectional view on the line H of Figure 1 showing the shape of the lower portion of the receptacle.

A receptacle or hopper it is adapted to hold a quantity of the mixture to be sprayed, this hopper being provided with cover means 82 mi mally open but which may be closed for cleaning purposes as will be described hereinafter. Attached to and opening into the lower side of the receptacle it is an elongated tubular member i l to which is attached at its outer end an extension it of slightly smaller diameter. Extending laterally from the extension it is a nozzle 08. Surrounding the tubular member it and in spaced relation thereto is a tube or sleeve it which is also provided with an extension-22 oi smaller diameter and which extension sur-= rounds the major portion of the smaller extension The extension 22 is provided with an opening 23 through which the nozzle it projects. The

end of the smaller extension is adapted to be" closed as by a screw is having a washer 28 which abuts against and serves to close the otherwise open end of the larger extension 22. A compressed air line 28 containing a valve 36 is con-: nected to the outer tube 20 and a branch 32 of the compressed air line leads to the upper portion of the receptacle it, this branch also containing a valve 34.

Extending from the lower portion of the receptacle l0 and in alignment with the tubular member [4 is a short tube or pipe 36. An elongated flat or ribbon-shaped agitating member or rod 38 extends through the tube 3B,.the lower portion of the receptacle l and thetubular member I4 and is connected at the end b means of the coupling 40 to the shaft of a small motor 42. The outer end of the tube 36 is provided with a stuillng box M or gland. Connected to the other end of the agitating member 38 as by solder is a small helical spring as of a length such that it extends through the small tubular extension l6 and abuts against the inner end or the screw 24. The lower portion of the receptacle I0 is tapered at 68 as shown more clearly in Figure 4.- so that the mixture within th receptacle will move downwardly toward the agitating member 38. The width of the member as is but slightly less than the inner diameter of the tubular member it! so that when this member is rotated [it will not only agitate the materlal within the tubular member M but will scrape from the inner surface of this member any of the material to be sprayed which might otherwise adhere thereto. Since the agitating member 38 is ribbon-shaped or flat it will, as it is rotated, tend to assume a spiral shape and be cause of this it may impart a. small movement to the surrounding material in a direction toward the nozzle i 8. Likewise the small spring 36 is preferably wound in such manner that when it is rotated it, too, will tend to move the surrounding material along toward the end of the tubular extension It to which the nozzle i8 is afiixed.

It is important that the nozzle l8 projects into or through the opening 23 in the tubular exten= sion 22 to an extent such that compressed air issuing outwardly through the opening 23 will entrain the material passing downwardly through the nozzle 88 so that a proper spray will result. If the nozzle projects too far through the opening 23 the material in the nozzle will not be picked up by the jetting air to the proper degree and if the nozzle does not extend or project far enough through the opening 23 some of the compressed air will pass backwardly through the nozzle and then through the tubular mem-- bers l6 and M to the container ill. In either case an unsatisfactory spray will be the result. In order to adjust the position of the tubular extension is and thus the position of the nozzle IS with respect to the surrounding tubular member 22 and its opening 23 a plurality, three in this instance, of screws 50 are threaded into the extension 22 as shown in Figure 3 and'are so dis= posed that their inner ends abut against the tube l6. By loosening the upper screws and tightenrigidly in its predet rmined position with respect to the outer tube 22.

In operation, the mixture to be sprayed is placed in the receptacle ID and the motor 42 energized to rotate the agitator 38 until the mixture has passed through the tubes l4 and It to the nozzle IS. The valve an is then opened and compressed air passing through the outer tube and downwardly through the opening 23 entrains the mixture from the nozzle and produces a jet or spray directed laterally. The screws 50 will be manipulated until the most effective spray is produced and the device will then be ready for use. During the spraying operation the cover l2 0! the receptacle l0 will be removed or held open as shown in Figure 1 and the valve 34 in the compressed air pipe 32 will be closed. After the spraying operation has been completed the cover l2 may be closed and the valve 34 opened in order to admit compressed air to the receptacle l0 above any remaining mixture contained therein so as to blow the mixture outwardly through the nozzle l8 to eilect the cleaning of the device. Shown as connected to the outer tube 20 is an inlet 52 containing a valve 54. If desired, a suitable solvent such as acetone may be passed into the outer tube 20 through this inlet in order to aid in cleaning the interior of the device.

As has been mentioned hereinbeiore the device which has been described is particularly suitable for spraying a mixture made up of very small particles of a hard material in a low viscosity liquid adhesive onto the inner surfaces of tubes to be used as cathodes in proportional counters for detecting neutrons. Particles of boron carbide averaging one mil or less in diameter have been mixed with a suitable adhesive such as Duco cement thinned with a suitable solvent such as acetone, and the mixture then sprayed onto the inner surface of metal tubes until a substantially uniiorm coating or layer averaging from 0.0001 to 0.005 inch has been obtained. These cathode tubes are often two or three feet or more in length and often have an internal diameter of as little as one-half inch or even less. Such a tube may be mounted in the chuck of a lathe, th spraying device being mounted on the lathe platform so that the end containing the nozzle Hi can be passed back and forth within and throughout the length of the rotating tube. In one of the spraying devices which has been used successfully the outside diameter of the outer tube 20 is only slightly over one-fourth inch and the total length of the tube 20 is about 30 inches. It has been found that with this device uniform coatings of boron carbide particles can be placed on the inside of small diameter metal tubes and that the spray jet is so uniform during the spraying operation that a very uniform coating results. In the spray guns which have been constructed and mentioned above the diameter of the opening of the nozzle 18 is about 5 mils.

In spraying a mixture of small hard particles in a low viscosity liquid such as sand and water or boron carbide and a liquid adhesive it is not possible to use a pressure gradient to force the mixture out of the nozzle as this pressure mainly accelerates the liquid and not the solid particles causing blocking at the nozzle. Where, however, a jet of compressed air is used to entrain the mixture to be sprayed which mixture is moved to the jet substantially by gravity, a very efiicient operation results.

Although the device has been described with reference to the coating of neutron detector cathodes with boron carbide it is to be understood the device will have many other uses and in many cases it will not, of course, need to be as small in diameter as that which has been described.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, but only such limitations should be imposed as are indicated in the appended claims.

' lclaimz' )1: A device for spraying heavy particles imaura-2c mersed in a low viscosity liquid which comprises a tubular member closed at one end, a receptacle for the mixture of particles and liquid communicating with the other end of said member, an agitating element extending through said receptacle and said tubular member, means for rotating said agitating element, a tube for compressed air disposed around in spaced relation and substantially enclosing said tubular member, said tube being provided with an opening near the closed end of said tubular member, a nozzle projecting laterally from said tubular member and extending through the opening in said tube sothat air jetting from said tube through the opening will entrain the mixture from said nozzle, and means for adjusting the position of said nozzle in said openmg.

2. A device for spraying a mixture of fine particles of a substance immersed in a low viscosity liquid onto the inner surface of a cylinder which comprises an elongated tubular member closed at one end and adapted to pass axially into and out of said cylinder during the spraying operation, a receptacle for the mixture communicat ing with the other end of said member, a nozzle projecting laterally from said member near'said closed end, an agitating element extending through said receptacle and said tubular member, means for rotating said agitating element, a tube for compressed air disposed around in spaced relation and substantially enclosing said tubular member, said tube being provided with an opening slightly larger than and through which said nozzle extends so that air outwardly from said tube through said opening will entrain said mixture from said nozzle and deposit it on the inner surface of said cylinder, means for adjusting the position of the outer portion of said tubular member with respect to the surrounding compressed air tube so as to control the position of the outer end of the nozzle within said opening, said adjusting meansv comprising at least one screw member threaded radially through said tube and bearing at its inner end against said tubular member.

3, A device for spraying a mixture of heavy particles of a substance immersed in a low viscosity liquid which comprises a tubular member closed at one end, a receptacle for said mixture mounted above and in communication with the other end of said member, a nozzle projecting laterally from said member near said closed end,

an elongated ribbon-shaped agitating element extending through the lower portion of said receptacle and axially through said tubular memher. means on the outer end of said element in proximity to said nozzle for stirring the mixture just before it passes through said nozzle, said last named means comprising a coil spring attached at one end to the outer end of said agitating element and extending past the inner end or said nozzle, means for rotating said agitating ele-: ment, a tube for compressed air disposed around in spaced relation and substantially enclosing said tubular member, said tube being provided with an opening slightly larger than, and through which said nozzle extends, a cover for the top of said receptacle and valved means for directing compressed air to the upper part of said receptacle so that the mixture within the tubular member can be blown out through the nozzle and the tubular member and the nozzle thereby cleaned.

4. A device for spraying a mixture of finely divided particles of boron carbide in a low viscosity liquid adhesive onto the inner surface of a horizontal rotating cylinder which comprises a tubular member closed at one end and adapted to be passed longitudinally back and forth along the axis of said cylinder, a receptacle for said mixture communicating with and extending above the other end of said tubular member, a capillary nozzle projecting downwardly from said member near said closed end, means for agitating said mixture within said receptacle and said tubular membercomprising an elongated ribbon-shaped rod extending through the lower portion of said receptacle and through said tubular member, means for rotating said rod about its longitudinal axis, and a tube for compressed air disposed around in s aced relation and substantially enclosing said tubular member, and said nozzle, said tube being provided with an opening slightly larger than, and through which said nozzle extends, the arrangement being such that compressed air emitted through said opening past said nozzle will entrain said mixture and spray it onto said cylinder surface.

JOHN THAD REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,427,455 Gates Aug. 29, 1922 1,971,535 Perkins Aug. 28, 1934 2,403,994 Paynter July 16, 1946 

